Technical Field
The present invention relates generally to boost converter circuitry and, more specifically, to a boost converter circuit that is able to perform a low-power startup and maintain efficient operation with a decreased power supply.
Introduction
Boost circuits are typically designed to receive an input voltage and produce an output voltage greater than the input voltage. Such an example boost circuit is illustrated in FIG. 1, wherein the example boost circuit 100 comprises an internal LDO regulator circuit 102 whose power supply node is connected to a power supply 104. However, because the internal circuitry in the example boost circuit 100 in FIG. 1 is powered by the power supply 104 in the form of a battery, this circuit 100 is particularly susceptible to reduction of the power supply 104. As such, the circuit 100 in FIG. 1 is more suitable for higher-voltage power supplies such as, for example, lithium-ion batteries having a voltage supply of approximately 3-5V, and not low-voltage power supplies such as, for example, those within a range of approximately 1.2V to 1.5V.
FIG. 2 illustrates another example boost circuit 200, wherein the internal LDO regulator circuit 202 is powered at its power supply node by the output voltage produced by the boost circuit 200. Although the circuit 200 in FIG. 2 may provide a solution to the internal circuitry power supply issues present in the circuit 100 in FIG. 1, the circuit 200 in FIG. 2 requires a relatively high supply voltage to maintain operation after it starts up. As such, the circuit 200 in FIG. 2 is particularly vulnerable to a decrease in the supply voltage 204 after start-up, and therefore, is not a practical solution for applications in which the supply voltage 204, for example, from a battery, decreases during normal operation of the boost circuit 200.
FIG. 3 illustrates another example boost circuit 300, wherein the example boost circuit 300 omits the internal regulator circuitry and, instead, couples the power supply node of its internal boost circuitry 302 directly to the power supply 304. FIG. 4 illustrates yet another example boost circuit 400 similar to the example boost circuit 300 in FIG. 3, but where the power supply node of the internal boost circuitry 402 is coupled directly to the output voltage of the boost circuit 400. The example embodiments illustrated in FIGS. 3 and 4 are designed to allow for easier start-up of the respective boost circuits; however, these circuits are sensitive to external interference. For example, when the internal resistance of the power supply is relatively large (e.g., 0.5 ohms), the boost circuit 300 in FIG. 3 experiences a significant decrease in boost efficiency, typically caused by a decrease in the voltage driving an output transistor 306 as the output current of the circuit 300 increases. Additionally, the boost circuit 300 in FIG. 3 fails during low-power operation when the voltage at the power supply 304 experiences a significant decrease. The boost circuit 400 in FIG. 4 becomes unstable when a load transient jump occurs at its output, causing the output of the circuit 400 to oscillate. As such, conventional boost converter circuitry such as, for example, that described above and illustrated in FIGS. 1-4, fails to provide low-power start-up and efficient low-power operation.